The long-term goal of Project 1 is to identify mechanisms responsible for more efficient DNA repair in long-lived species. Accumulation of somatic mutations and genomic rearrangements is believed to be a contributing cause of aging. Genomic rearrangements, arising from errors during repair of DNA breaks are a characteristic feature of aged tissues. DNA double-stranded breaks (DSBs) are repaired by two pathways homologous recombination and non-homologous end joining. Our preliminary data indicate that the efficiency of both NHEJ and HR pathways strongly correlates with maximum lifespan. We have also demonstrated that SIRT6 protein is an upstream regulator of both NHEJ and HR pathways and is the only factor capable of stimulating both pathways of repair, and of rescuing the declining NHEJ and HR in senescent human cells. We hypothesize that variations in SIRT6 function contribute to the differences in DSB repair across species. Our objectives are to characterize the differences in SIRT6 function between short- and long-species, as well as to identify novel factors responsible for more efficient DSB repair in long-lived species. We propose to: (1) perform detailed biochemical analysis of SIRT6 from 18 rodent species and identify the properties that distinguish SIRT6 in long-lived species; test, in collaboration with Project 3, whether more efficient SIRT6 function in long-lived species leads to lower mutation loads; (2) Identify the differences in upstream regulation of SIRT6 and its downstream targets between the short- and long-lived rodents; (3) Characterize, in collaboration with Project 4, novel DSB repair genes that contribute to more efficient DSB repair in long-lived species. Gore B will provide access to primary cell collections and Core C will assist with statistical analysis and sequence analysis of newly cloned genes. The results of Project 1 will determine the mechanisms responsible for more efficient DNA DSB repair in long-lived species. Furthermore, Project 1 in collaboration with the other three Projects of this PPG will identify potential targets for intervention aimed at extending lifespan and preventing cancer.